Synthesis and characterization of palladacyclopentadiene complexes with N-heterocyclic carbene ligands

New palladacyclopentadiene compounds containing different chelate NHC-thioether and NHC-pyridine ligands have been prepared by transfer of the functionalized carbenes from the respective silver complexes to the polymeric precursors [PdC-COOR)4]n (R = Me, t-Bu). Their dynamic behaviour in solution was discussed and the solid-structure of 2c was determined by X-ray crystallography. The treatment of [Pd(C-COOCH3)4]n with two equivalents of the carbene silver complexes led to the (NHC)2Pd(C4-COOCH3)4 derivatives (3cei), a new class of compounds with only PdeC bonds. A serious limitation to this synthetic procedure is an excessive steric crowding around the metal centre. The complexes 3 are present in solution as a mixture of two atropoisomers, due to restricted rotation around the CarbeneePd bond. The kinetics of equilibration between the two configurational isomers was studied for complex 3c, which was also structurally defined by X-ray crystallography (anti isomer). Finally a synthetic protocol was set up for the synthesis of mixed NHC-Phosphine and NHC-Isocyanide palladacyclopentadiene complexes. In this procedure the order of addition of the reactants is of great importanc

DNA/protein binding and magnetic properties of a 1D Cu(II) complex containing fumarate and tridentate Schiff base ligands

ID copper(II) complex, [Cu2(L)2(fum)]∙H2O}n (1) has been synthesized using fumarate (fum2-) and a Schiff base (HL), derived from the condensation reaction of 2-amino-1-butanol and salicyldehyde. Complex 1 has been characterized by X-ray crystal structure, FT-IR, electronic absorption and fluorescence spectroscopic methods. The structural determination reveals that complex 1 crystallizes in the monoclinic system with space group P21/n and form 1D polymeric chain, built by bridging fum. Weak π¿π and C-H¿π interactions in 1, lead to a 3D supramolecular architecture. Complex 1 exhibits fluorescence at room temperature with a quantum yield (Φs) of 0.257. The interactions of complex 1 with bovine serum albumin (BSA) and human serum albumin (HSA) were studied using electronic absorption and fluorescence spectroscopic techniques and the analysis shows that complex 1 interaction with BSA / HSA occurs mainly with ground state association process. Calculated values of apparent association constants are 1.34 × 104 M-1 and 1.81 × 104 M-1 for BSA and HAS, respectively, at 300 K. The number of binding sites and binding constants were calculated using double logarithm regression equation. The interaction of complex 1 with the calf thymus DNA (CT-DNA) was also investigated using electronic absorption and fluorescence spectroscopic methods. The results show that complex 1 has binding affinity to CT-DNA in the order of 2.96×105 M-1. Low temperature magnetic measurements reveal existence of antiferromagnetic interaction in complex 1. The magnetic data have been fitted considering complex 1 as a pseudo-dinuclear system, with the two copper(II) atoms bridged by two carboxylate oxygen atoms, since the coupling through long fum bridge is almost nil. The best-fit parameters obtained with this model are J = - 60 cm-1, gCu = 2.20

Strategic synthesis of [Cu2], [Cu4] and [Cu5] complexes: inhibition and triggering of ligand arm hydrolysis and self-aggregation by chosen ancillary bridges

The Schiff base ligand HL1 ({2,6-bis(allylimino)methyl}-4-methylphenol) having no coordinating donor arm has been examined for its reaction medium and ancillary bridge dependent reactivity for hierarchical family of CuII complexes. The ligand showed unique reactivity pattern toward CuII in solution. The bridging nature of in situ generated HO− ions in absence and presence of externally added carboxylates (RCOO−; R= CF3, C6H5 and CH3) has been utilized to produce complexes {[Cu2(µ–L2)2(H2O)]2[Cu2(µ–L2)2(H2O)2](ClO4)6} (1) (HL2 = 3-{(allylimino)methyl}-2-hydroxy-5-methylbenzaldehyde), [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CCF3)4] (2), [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CC6H5)4]∙H2O (3), [Cu5(µ3–OH)2(µ–L1)2(µ1,3–OAc)2(OAc)2(H2O)4][Cu5(µ3–OH)2(µ–L1)2(µ1,3–OAc)2(OAc)3(H2O)](ClO4)3∙2C2H5OH (4). Absence of carboxylate anions did not yield HO− ions in situ and triggered single ligand arm hydrolysis. The formation of tetra- and pentanuclear aggregates as well as ligand hydrolyzed dinulcear products has been rationalized to identify the possible roles of carboxylate anions in solution. Detailed characterization of the complexes in the solid state and in solution have been carried out using spectroscopic measurements, X-ray crystallography, variable temperature magnetic measurements and functional behavior. In MeOH solutions at 298 K, the complexes 1-4 showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) saturated with O2 of air

Structural and magnetic characterization of three tetranuclear Cu(II) complexes with face-sharing-dicubane/double-open-cubane like core framework

Three novel tetranuclear copper(II) complexes namely [Cu4(L1)4]∙(dmf) (1), [Cu4(L1)4] (2) and [Cu4(L2)2(HL2)2(H2O)2]∙2(ClO4)∙6(H2O) (3) (H2L1, (E)-2-((1-hydroxybutan-2-ylimino)methyl)phenol; H2L2, (E)-2-((1-hydroxybutan-2-ylimino)methyl)-6-methoxyphenol)) were synthesised from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligands. The structural determination reveals that complex 1 crystallizes in the monoclinic system with space group C2/c, whereas both the complexes 2 and 3 crystallize in the triclinic system with space group P-1. Complexes 1 and 2 possess face-sharing dicubane core, on the other hand complex 3 has double open cubane core structure. The copper(II) ions in the cubane core are in distorted square planar geometries, and weak π¿π and C-H¿π interactions lead to formation of a 2D supramolecular architecture for complexes 1 and 2. At room temperature complexes 1, 2 and 3, exhibit fluorescence with a quantum yield (Φs) of 0.47, 0.49 and 0.38, respectively. Variable temperature magnetic susceptibility measurements in the range 2-300 K indicate an overall weak antiferromagnetic exchange coupling in all complexes. The PHI program was used to study their magnetic behaviour. In agreement with their face-sharing dicubane structure, a Hamiltonian of the type H = - J1(S1S2+S1S2'+S1'S2+S1'S2') - J2S1S1', where S1 = S1' = S2 = S2' = SCu = 1/2, was used for studying complexes 1 and 2. Simulations performed suggest magnetic exchange constants with values close to J1 = -20 cm-1 and J2 = 0 cm-1 for these complexes. On the other hand, the spin Hamiltonian H = - J1(S1S4+S2S3) - J2(S1S3+S2S4) - J3S1S2, where S1 = S2 = S3 = S4 = SCu = 1/2, was used to study the magnetic behaviour of the double open cubane core of complex 3 and a good agreement between the experimental and simulated results was found by using the parameters g1 = g2 = 2.20, g3 = g4 = 2.18, J1 = -36 cm-1, J2 = -44 cm-1 and J3 = 0 cm-1

Metallacrowns of Ni(II) with alpha-aminohydroxamic acids in aqueous solution: beyond a 12-MC-4, an unexpected (vacant?) 15-MC-5

Growing attention has been devoted in the recent years to a class of metallamacrocycles known as metallacrowns (MCs). They are structural analogues of crown ethers where the methylene bridges have been substituted by coordinative bonds formed by a transition metal ion ("ring" metal) and a nitrogen atom. The cavity of the metallacrown can accommodate an additional metal ion ("core" metal) either identical or different from the ring metal, thus forming a homo- or hetero-metallic MC. The most studied ring metal ion is certainly Cu(2+) and the aminohydroxamic acids have proved to be very suitable ligands to form MCs. The behavioural analogies between Cu(2+) and Ni(2+) in forming complexes, along with recent literature data in the solid state, prompted us to investigate the possible MC formation between Ni(2+) and both (S)-α-alaninehydroxamic acid and (S)-valinehydroxamic acid, in aqueous solution. Two metallacrowns, a 12-MC-4 and an unexpected 15-MC-5 have been detected by potentiometry and confirmed by ESI-MS results. Their structures are discussed on the basis of potentiometric, calorimetric, spectroscopic data and DFT calculations. The existence of a vacant 15-MC-5 species in solution can be put forward for the first time, making the present metal/ligand systems very interesting for their potential applications in cation recognition and separation. Finally, the crystal structure of the binary complex K[NiL(2)H(-1)]·5/3 H(2)O of (S)-α-alaninehydroxamic acid (LH) is also reported

Isocyanide insertion across the Pd–C bond of allenyl and propargyl palladium complexes bearing phosphoquinoline as a spectator ligand. Synthesis of a palladium complex bearing a coordinated cyclobutenyl fragment

We have studied the insertion of p-toluenesulfonylmethyl isocyanide (TosMIC) on selected allenyl and propargyl complexes of palladium bearing diphenylphosphine quinoline as a spectator ligand. The fast process gives different products depending on the tautomer involved in the reaction. Thus, the unsubstituted allenyl species yields an insertion complex with the isocyanide coordinated between the metal and the first allenyl carbon. On the other hand, a mixture of phenyl substituted allenyl and propargyl palladium complexes yields a novel species characterized by a cyclo-butenyl fragment directly coordinated to palladium. The solid state structure of such a complex together with an exhaustive kinetic study of the whole process is reported

The unexpected case of reactions of halogens and interhalogens with halide substituted Pd(II) sigma-butadienyl complexes

We have experimentally studied and theoretically interpreted the addition under stoichiometric conditions of halogens or interhalogens to sigma-butadienyl palladium complexes bearing the heteroditopic thioquinolines as spectator ligands. The observed reactions do not involve the expected extrusion of the butadienyl fragment but rather the unpredictable substitution of the halide coordinated to palladium and in some cases also of that bound to the terminal butadienyl carbon. We have explained this peculiar reactivity with a mechanistic hypothesis based on a sequence of selective processes of oxidative addition and reductive elimination involving Pd(IV) intermediates

correction on the stability of manganese tris β diketonate complexes as redox mediators in dsscs

Correction for 'On the stability of manganese tris(β-diketonate) complexes as redox mediators in DSSCs' by Stefano Carli et al., Phys. Chem. Chem. Phys., 2016, 18, 5949–5956

Interplay between steric and electronic factors in determining the strength of intramolecular resonance-assisted NH...O hydrogen bond in a series of [beta]-ketoarylhydrazones

Publisher's version/PDFThe crystal structures of six [beta]-ketoarylhydrazones are reported: 1,(Z)-2-(2-bromophenylhydrazono)-3-oxobutanenitrile; 2, (Z)-2-(2-methylphenylhydrazono)-3-oxobutanenitrile; 3, (E)-methyl-2-(2-methoxyphenylhydrazono)-3-oxobutanoate; 4, E, methyl-2-(2-cyanophenylhydrazono)-3-oxobutanoate; 5, (Z)-methyl-2-(4-cyanophenylhydrazono)-3-oxobutanoate; 6, pentane-2,3,4-trione-3-(2-carboxyphenylhydrazone). All of them form intramolecular hydrogen bonds assisted by resonance (RAHB), with N...O distances in the range 2.541(5)-2.615(3) [Angstrom]. These hydrogen bonds are differently aff ected by the substituents at the heterodienic fragment, being strengthened by electronwithdrawing substituents in position 2 (more by 2-COMe than 2-CN substitution), and weakened in [beta]-esterhydrazones and when the N-H forms a bifurcated hydrogen bond. The role played by the different steric and electronic properties of the substituents in strengthening the H-bond is investigated, besides X-ray crystallography, by IR and [superscript 1]H NMR characterization of the NH proton, and quantum mechanical DFT calculations at the B3LYP/6-31 + G(d,p) level of theory on test molecules